From a6838bbc6726ad624bd2b94991f690b8e9d23c69 Mon Sep 17 00:00:00 2001 From: Javier Martinez Canillas Date: Thu, 10 Sep 2020 17:17:57 +0200 Subject: [PATCH] tftp: Roll-over block counter to prevent data packets timeouts Commit 781b3e5efc3 (tftp: Do not use priority queue) caused a regression when fetching files over TFTP whose size is bigger than 65535 * block size. grub> linux /images/pxeboot/vmlinuz grub> echo $? 0 grub> initrd /images/pxeboot/initrd.img error: timeout reading '/images/pxeboot/initrd.img'. grub> echo $? 28 It is caused by the block number counter being a 16-bit field, which leads to a maximum file size of ((1 << 16) - 1) * block size. Because GRUB sets the block size to 1024 octets (by using the TFTP Blocksize Option from RFC 2348 [0]), the maximum file size that can be transferred is 67107840 bytes. The TFTP PROTOCOL (REVISION 2) RFC 1350 [1] does not mention what a client should do when a file size is bigger than the maximum, but most TFTP hosts support the block number counter to be rolled over. That is, acking a data packet with a block number of 0 is taken as if the 65356th block was acked. It was working before because the block counter roll-over was happening due an overflow. But that got fixed by the mentioned commit, which led to the regression when attempting to fetch files larger than the maximum size. To allow TFTP file transfers of unlimited size again, re-introduce a block counter roll-over so the data packets are acked preventing the timeouts. [0]: https://tools.ietf.org/html/rfc2348 [1]: https://tools.ietf.org/html/rfc1350 Fixes: 781b3e5efc3 (tftp: Do not use priority queue) Suggested-by: Peter Jones Signed-off-by: Javier Martinez Canillas Reviewed-by: Daniel Kiper --- grub-core/net/tftp.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-) diff --git a/grub-core/net/tftp.c b/grub-core/net/tftp.c index 644135caf..7e659a78b 100644 --- a/grub-core/net/tftp.c +++ b/grub-core/net/tftp.c @@ -183,11 +183,22 @@ tftp_receive (grub_net_udp_socket_t sock __attribute__ ((unused)), return GRUB_ERR_NONE; } - /* Ack old/retransmitted block. */ - if (grub_be_to_cpu16 (tftph->u.data.block) < data->block + 1) + /* + * Ack old/retransmitted block. + * + * The block number is a 16-bit counter, thus the maximum file size that + * could be transfered is 65535 * block size. Most TFTP hosts support to + * roll-over the block counter to allow unlimited transfer file size. + * + * This behavior is not defined in the RFC 1350 [0] but is implemented by + * most TFTP clients and hosts. + * + * [0]: https://tools.ietf.org/html/rfc1350 + */ + if (grub_be_to_cpu16 (tftph->u.data.block) < ((grub_uint16_t) (data->block + 1))) ack (data, grub_be_to_cpu16 (tftph->u.data.block)); /* Ignore unexpected block. */ - else if (grub_be_to_cpu16 (tftph->u.data.block) > data->block + 1) + else if (grub_be_to_cpu16 (tftph->u.data.block) > ((grub_uint16_t) (data->block + 1))) grub_dprintf ("tftp", "TFTP unexpected block # %d\n", tftph->u.data.block); else {